Conventionally, spot welding has been widely used as one means of welding body workpieces of cars, wherein, with electrode tips attached to a welding gun making pressure contact with the workpieces, electric current is applied, so as to melt and fuse the metal with the resistance heat. Performing the spot welding for a long time causes the electrode tips to suffer deformation and wear of the tip shape, making it harder to secure required welding quality. Therefore, it has been the practice that, when a certain amount of processing time or a certain number of welding points is exceeded, the electrode tips are removed from the welding gun and replaced with new electrode tips, so as to secure a good tip shape of the electrode tips.
Recently, many of the materials to be welded together are provided with rust proof treatment or the like using chemicals, because of which electrode tips tend to wear more quickly and need to be replaced more frequently. However, stopping the welding process line each time for the operator to change the electrode tips would lower the production efficiency. Therefore, it has been the practice to install an electrode tip mounting/dismounting apparatus on the welding process line and to move a robot arm so as to move the welding gun attached to the robot arm to a position where the electrode tip mounting/dismounting apparatus is installed, so that the electrode tips of the welding gun are changed by means of the electrode tip mounting/dismounting apparatus. This electrode tip mounting/dismounting apparatus is constituted by an electrode tip removing apparatus that removes the electrode tips from the welding gun, and an electrode tip magazine that stores a plurality of electrode tips. In the conventional structure, the electrode tip magazine stores a plurality of electrode tips in the up and down direction such that they are biased by a coil spring thereby to be supplied one by one to supply ports that open to the upper side and the underside. However, one problem was that, the biasing force of coil springs was not constant depending on the compression strength, i.e., the coil spring would exert a smaller biasing force in a state when the compression length was short, in which case the electrode tips would fall off from the supply port that opened to the underside of the electrode tip magazine.
In view of this, the applicants of the present application have proposed an electrode tip magazine for a spot welder shown in Patent Document 1. This electrode tip magazine for a spot welder shown in Patent Document 1 is structured, as shown in FIG. 25, such that a spiral spring 52 is mounted on the side of the supply port 51a of a rack body 51 to pull a push-out member 53 by the spiral spring 52 so as to supply the electrode tips 55 one by one by pushing them out from the supply port 51a with the push-out member 53 by the spiral spring 52. With this structure in which the push-out member 53 is pulled by the spiral spring 52, the biasing force is made almost constant, whereby it is unlikely that the electrode tips 55 fall off from the supply port 51a. 
However, because of the structure in which the push-out member 53 is pulled by the spiral spring 52, the spiral spring 52 is mounted on the side of the supply port 51a, increasing the size around the supply port 51a. This would sometimes cause the problem that, depending on the type of the welding gun, the part where the spiral spring 52 was mounted interfered with the welding gun. This problem was usually solved by producing an electrode tip magazine for a spot welder that was specially customized such as attaching the spiral spring 52 beside the supply port 51a so that the magazine would not interfere with the welding gun. Producing electrode tip magazines for a spot welder in accordance with the shapes of welding guns to be used like this would cause the problem of a very high cost.    Patent Document 1: Japanese Published Unexamined Patent Application No. 2006-68787